The present invention relates to improvements in an anti-creep control apparatus of an automatic transmission of a vehicle.
Various anti-creep control apparatus of an automatic transmission have been proposed in order to decrease vehicle body vibration and energy consumption during idling of the vehicle and to prevent a so-called creep phenomenon that the vehicle is moved forward inch by inch without acceleration of the engine when the automatic transmission is put in a drive range. Japanese Patent Provisional Publication No. 5-157173 discloses a typical anti-creep control apparatus of an automatic transmission which apparatus is arranged to quickly engage a forward clutch if a driver intends to quickly start the vehicle and to slowly engage the forward clutch so as to decrease a shock in the clutch releasing operation if a driver does not intend to quickly start the vehicle.
However, when a command hydraulic pressure of the forward clutch is decreased in accordance with the start of the anti-creep control of this conventional anti-creep control apparatus, the command hydraulic pressure is put in an undershoot condition as shown by a dotted line of FIG. 6 because of a time delay of the increase of the torque converter output rotation speed and of the hysteresis in characteristics between the hydraulic pressure and a piston stroke. If a driver tries to quickly start the vehicle by depressing an acceleration pedal during this undershoot of the forward clutch hydraulic pressure, the engagement of the forward clutch is delayed by the degradation of the responsibility of the increase of the forward clutch hydraulic pressure. This invites a racing of an engine of the vehicle and a shock by the engagement of the forward clutch thereafter.